This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/EP99/02558 which has an International filing date of Apr. 15, 1999, which designated the United States of America.
This invention relates to a process to produce polyols and to polyols as defined in claim 1.
It is well known in the art to dissolve polyurethane foams in low molecular weight glycols and thus to produce polyols for the production of polyurethane rigid foams. It is further known to cleave the urethane group by strongly basic aliphatic amines to react them into substituted urea groups.
In U.S. Pat. No. 4,162,995 e.g. the simultaneous glycolysis and ammonolysis of polyurethanes by glycols, polyols, ammonia or ammonium hydroxide to form a mixture of polyols is described in which the resultant amines are either separated or further processed. According to this invention a second step in the procedure and only the use of ammonia is allowed. In U.S. Pat. No. 3,404,103 a process is described for the simultaneous alcoholysis and ammonolysis with pressure in the presence of methanol and ammonia at elevated temperature to produce a mixture of polyols and amines and ureas, resp., which are separated after cleavage of the macromolecules. To accelerate the ammonolysis strongly basic catalysts are further added to the reaction mixture. In this process a pressure step and the work-up (separation of methanol, catalysts and excess ammonia)of the polyols are necessary before further processing. The catalysis by tertiary amines of the glycolysis is described e. g. in DE-PS 27 38 572. According to U.S. Pat. No. 3,708,440 dialkanol amines and aliphatic diols are used together to solvolyse polyurethane rigid foams and polyisocyanurate foams at elevated temperatures. U.S. Pat. No. 4,110,266 relates to the reaction of polyurethane rigid foams or polyisocyanurate foams with alkanolamines, the separation of any excess of them and the use of the reaction mixture as starter of polyols. U.S. Pat. No. 3,117,940 is directed to the exclusive use of primary aliphatic amines for the aminolysis of polyurethane waste.
In the processes described in said patents it is disadvantageously attempted to enhance the comparably low basicity of the alcohols, amino alcohols and ammonia, resp., by adding further catalysts to result in useful reaction times for cleaving polyurethanes.
Object of the present invention is to provide an improved process to produce polyols from polyurethane wastes as well as polyols according to this process to produce polyurethanes from them.
According to the present invention polyurethane wastes are introduced into a mixture of at least one diol and at least one secondary alkyl amine and reacted at temperatures in the range of 120 to 220xc2x0 C. by which process a mixture of polyether alcohols and substituted polyureas dissolved or dispersed in them is formed.
The ratio of diol and amine depends on several parameters among which the average molecular mass of the reactants and the type of polyurethane are most essential. It should be kept in mind that the secondary alkyl amine is both catalyst of the depolymerization reaction and reactant and hence must not be used in excess. If related to the diol and polyurethane present the amine used may be varied in a broad range of mass ratios which range about to 100:100:50 as a lower limit and 100:25:5 as an upper limit for the ratio of polyurethane:diol:amine. Advantageously, a range of 100:50:25 to 100:25:6 is used. Depending on the type of polyurethane, the reaction product nearly does not contain free amine making further work-up not neccessary.
Surprisingly it was found that polyurethane wastes, especially polyurethane foam wastes, dissolve comparably rapidly in mixtures of a diol and a secondary alkyl amine and lead to polyol mixtures so far suitable ratios of reactants are used. The polyol mixtures can be used to produce semi-rigid foams, rigid foams, coatings, or adhesives.
The polyols of the invention are favorably produced by reacting polyurethane soft foams by their successive introduction into a mixture of a lower poly(alkylene glycol) and a secondary alkyl amine at a temperature ranging from 120xc2x0 C. to 220xc2x0 C. Alternatively, the process of the invention may be carried out by gradually reacting polyurethane rigid foams in a mixture consisting of a lower poly(alkylene glycol) and a secondary alkyl amine at temperatures in the range of 120 to 220xc2x0 C.
A further embodiment of the present invention relates to the reaction of elastic polyurethanes or microcellular elastic polyurethanes in a mixture of a diol and at least one secondary alkyl amine at temperatures in the range of 120 to 220xc2x0 C. where the mixture of diol and amine is in the mass range of 1:2 to 1:9 and this mixture is in the ratio to the elastomeric polyurethane in a weight ratio up to 1:9.
Especially favored is a process according to the invention by which polyurethanes are reacted with a mixture of poly(alkylene glycol) of average molecular mass from 108 to 600 and a di-n-alkylamine with a chain length of the alkyl groups of 2 to 6 in a temperature range of 130 to 200xc2x0 C. Poly(alkylene glycol) fractions having an average molecular mass of 200, 300, 400, or 600 are preferred since these fractions show to be good solvents for the foams and the substitued ureas derived from the urethane groups and further act as cell opening agents during foaming and improve foam quality when used in the concentration according to the invention.
This invention shows several advantages.
The combination of glycolysis and aminolysis in the recycling of polyurethanes leads to a completely different reaction mechanism of the depolymerization of the polyurethanes compared to the state of the art glycolysis. During glycolysis the cleavage proceeds preferably by transesterifaction at the urethane groups and as secondary reactions with a nucleophilic cleavage of the polyureas and a decarboxylation of the urethane groups, both with the formation of primary aromatic amines. Contrary to this, by cleaving the polyurethanes by a combination of glycolic hydroxyl groups and secondary amino groups the urethane groups are transformed to trisubstituted urea groups and because of the basic reaction conditions a nucleophilic reaction at the urea groups of the polyureas takes place in the trace range. During the reaction of the combination of glycol and secondary alkyl amine with the polyurethane, hence, are produced mainly the long chain polyether alcohols from the polyurethanes and the polyureas from the isocyanate and the secondary alkyl amine, i.e. no free primary aromatic amines. The polyureas are present in the mixture of lower molecular weight glycol and long chain polyether alcohol in dissolved and/or dispersed form. By carrying out the process this way the resulting reaction mixture has not only a completely different composition but also the amount of glycol used may be drastically decreased and is, as shown in the examples, in the range of 50 to 20% of the amounts necessary during glycolysis according to the state of the art. By this process a composition of the polyether component results which for the first time allows the production of elastomeric polyurethanes, foams, elastomers, coatings and sealants from recycling polyols without a work-up step. The polyol component with a high percentage of long chain polyether alcohols after reaction with polyisocyanates moves the glass transition temperature of the resulting polyurethanes to lower values, i.e. at room temperature into the elastic region, and this value is not moved to markedly higher temperatures by the low content of low molecular weight diols. By chosing these low molecular weight diols according to the invention with respect to type and amount the upper and lower service temperature of the resultant polyurethanes may be controlled and predetermined already by the depolymerization reaction. Based on this the usage of higher molecular weight glycols in the glycol component is prefered in contrast to the state of the art while the propylene glycols starting with dipropylene glycol are especially suitable since their secondary hydroxyl groups are less reactive than the usual primary hydroxyl groups of the ethylene glycol series thus showing nearly the same reactivity as the hydroxyl groups of the long chain polyether alcohols. From these reasons, the polyols of the present invention show several advantages compared to the state of the art which are based on their specific properties and low cost production.
In a further embodiment of the present invention an economically favorable process is the use of technical non-purified amines or distillation residues from the amine synthesis of aliphatic amines.